1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine having a first fuel injection mechanism (an in-cylinder injector) injecting fuel into a cylinder and a second fuel injection mechanism (an intake manifold injector) injecting the fuel into an intake manifold or an intake port, and relates particularly to a technique for starting the internal combustion engine.
2. Description of the Background Art
An internal combustion engine having an intake manifold injector for injecting fuel into an intake manifold of the engine and an in-cylinder injector for injecting the fuel into a combustion chamber of the engine is known. When starting such an internal combustion engine, the fuel is injected into the intake manifold.
Japanese Patent Laying-Open No. 2001-073854 discloses a fuel injection control apparatus for an internal combustion engine of in-cylinder injection type that has a main fuel injection valve injecting fuel directly into a combustion chamber and an auxiliary fuel injection valve injecting the fuel into an intake manifold, and that is capable of reducing emission of uncombusted components in starting the engine to suppress undue fuel consumption. The fuel injection control apparatus according to Japanese Patent Laying-Open No. 2001-073854 includes: an auxiliary fuel injection valve controller causing the auxiliary fuel injection valve to start injecting fuel when the engine is started; and a main fuel injection valve controller prohibiting the main fuel injection valve from injecting the fuel for a period from a time point where the engine is started until a time point where the concentration of an air-fuel mixture formed in the combustion chamber by the fuel injected from the auxiliary fuel injection valve reaches at least a prescribed value, and allowing the main fuel injection valve to start injecting the fuel when the period has elapsed.
According to the fuel injection control apparatus, when the engine is started, the concentration of the air-fuel mixture formed in the combustion chamber by the fuel injected from the auxiliary fuel injection valve is awaited to be at least a prescribed value, and then the main fuel injection valve is allowed to start injecting the fuel. Therefore, a period from a time point where the main fuel injection valve starts injecting the fuel until a time point of initial combustion is shortened, or the main fuel injection valve starts injecting the fuel after initial combustion. This minimizes such an event that vaporization of the fuel injected from the main fuel injection valve is not facilitated and the fuel is accumulated in the combustion chamber in the liquid state, when starting the engine where the temperature thereof is low. Thus, emission of uncombusted components in starting the engine can be reduced and undue fuel consumption is suppressed.
However, according to the fuel injection control apparatus disclosed in Japanese Patent Laying-Open No. 2001-073854, the internal combustion engine is started while fuel is injected into the intake manifold to facilitate vaporization. Accordingly, if the temperature of the internal combustion engine is fully high, for example, vaporization may be unduly facilitated. In such a case, the air-fuel mixture is excessively high in ignitionability, which may lead to its self-ignition before being ignited by the spark plug (hereinafter also referred to as preignition) or to knocking. Accordingly, there has been a problem in establishing compatibility between prevention of preignition/knocking and prevention of occurrence of uncombusted fuel.